Device used in the excitation of substances for spectroscopic analysis

ABSTRACT

In a device which permits analysis of all the points of a filter or of a solid with the same degree of accuracy, a turntable placed beneath a vertical electrode serves as a support for the substance to be analyzed and is in turn supported by a laterally movable carriage. A motor which is mounted on the carriage serves to drive the turntable in rotation and to control the displacement of the carriage. The speeds of rotational and translational motion are controlled in such a manner as to ensure that the different points of the turntable pass opposite to the electrode along a spiral path and at constant speed.

United States Patent [72] lnventors PierreBlurn Grenoble;

Jean Spitz, Gieres, both ol, France [2|] AppLNo. 883,452

[22] Filed Dec. 9, 1969 [45] Patented June 8, 1971 (73] Assignee Commissariat A L'Energie Atomique Paris, France [32] Priority Dec. 18, 1968 [33] rance [54] DEVICE USED IN THE EXCITATION OF SUBSTANCES FOR SPECTROSCOPIC ANALYSIS UNITED STATES PATENTS 1/1952 Sandorffet al. 235/98 Primary Examiner- Ronald L. Wibert Assistant Examiner-1 L. Evans AttorneyCameron, Kerkam & Sutton ABSTRACT: In a device which permits analysis of all the points of a filter or of a solid with the same degree of accuracy, a turntable placed beneath a vertical electrode serves as a support for the substance to be analyzed and is in turn supported by a laterally movable carriage. A motor which is mounted on the carriage serves to drive the turntable in rotation and to control the displacement of the carriage. The speeds of rotational and translational motion are controlled in such a manner as to ensure that the different points of the turntable pass opposite to the electrode along a spiral path and at constant speed.

PATENIED JUN 8 I971 SHEET 3 [IF 3 ill l 'IIII DEVICE USED IN THE EXCI'IATION OF SUBSTANCES FOR SPECTROSCOPIC ANALYSIS This invention relates to a device for spectrographic analysis of substances, said device being particularly suited to analysis by spark spectrography.

A common method used, for example, in the determination of air contaminants in the atmosphere consists in collecting particulate matter by filtration of a known volume of air and then in subjecting the particles which have been collected on the filter to qualitative and quantitative analysis. The main object of this analysis is to detect the presence of metallic particles such as particles of thorium, uranium, beryllium or compounds of these latter which are particularly toxic when they are present in the form of aerosols as these are liable to penetrate into the human body through the respiratory tracts.

in practice, samples which are to be analyzed by the method of spark spectrography are placed on an electrically conducting support and brought opposite to an electrode. The formation of sparks between said electrode and the support causes ionization which depends on the nature of the sample to be analyzed. To this end, an analyzing device comprises a vertically fixed electrode and a sample-carrying turntable which is adapted to move beneath said electrode. Both the electrode and the turntable are connected respectively to the positive and negative poles of a high-voltage supply.

When the substances to be analyzed are distributed over a surface, it is necessary to place this surface beneath the electrode and to present each point of said surface opposite to the tip of said electrode. It is in fact extremely important to ensure that the entire surface is checked in order that not substance is liable to escape from inspection and especially in order to ensure that all points of said surface are subjected to strictly identical excitation by maintaining said points opposite to the electrode for exactly the same length of time.

The object of the present invention is to satisfy the requirement which has just been mentioned and to permit the displacement of the support for the substances to be analyzed in such a manner as to ensure that each point of said support is brought successively opposite to a stationary electrode for the same period of time.

This invention is directed to a device which comprises beneath a vertical electrode a turntable which is adapted to carry the substance to be analyzed and is mounted on a movable carriage, a motor which serves to drive the turntable in rotation about its own axis and at the same time to drive the carriage in rectilineal translational motion at right angles to said electrode so as to bring each point of the disc in turn beneath the electrode along a spiral path and means for controlling the speed of rotation of the motor in dependence on the lateral displacement of the turntable in order that the rate of transfer vertically beneath the electrode should be constant.

Each point of the support is thus brought in turn opposite to the electrode and is subjected to identical conditions of excitation. Substances of any kind can thus be detected and analyzed.

By means of a device of this type, it is therefore possible to analyze either the particles which are collected on a filter or a solution such as a metallic salt, chloride or other solution, after impregnation of a filter with said solution followed by drying of said filter. lt is even possible to determine the composition or homogeneity of a flat solid which is placed on the supporting turntable.

A number of additional advantages and properties of the invention will in any case become apparent from the following description of one embodiment which is given by way of example and not in any limiting sense, reference being made to the accompanying drawings, in which:

FIG. 1 shows diagrammatically the arrangement of the disc and of the electrode;

H6. 2 is a longitudinal sectional view of the analyzing device;

HO. 3 is a sectional view taken along line l-l of FIG. 2;

FIG. 4 is a diagram showing the system of control of the two movements of the device.

The analyzing device comprises a vertical electrode 1 and a turntable 2 which is placed beneath said electrode, as shown in HO. 1. The filter which serves as a support for the collected substances or the solid to be analyzed is carried directly by said turntable which is endowed in accordance with the invention on the one hand with rotational motion about its axis and on the other hand with lateral translational motion, the displacement of said turntable being carried out at right angles to the electrode 1.

The different points of the filter or of the solid then pass successively beneath the stationary electrode 1 along a spiral path. Both the turntable and the electrode are formed of a material which has good electrical conductivity such as graphite, for example, and is connected to a high-voltage electric circuit for producing either sparks or arcs in order to cause ionization or vaporization of the substance to be analyzed.

The spiral sweeping action is carried out with a pitch such that the total surface of the turntable 2 passes opposite to said electrode and that all the substances are thus detected.

Beneath the electrode 1 which is held in an electrode-holder 11 so as to permit only a vertical displacement of this latter for adjustment purposes, the turntable 2 is placed as shown in FIGS. 2 and 3 on a flat support 3, the lower portion of which is screwed onto an endpiece 4 forming an extension of a sleeve 5 fitted over a vertical rod 6 which is supported by a carriage 8, said rod being freely rotatable with respect to said carriage by means of a ball bearing 7. The sleeve 5 is fixed axially with respect to a second sleeve 15 which has an externally threaded end portion 9 and is engaged with a nut 10, said nut being applied against a bracket 12 which is rigidly fixed to the carriage 8. The sleeve 5 is freely rotatable within the interior of said sleeve 15 and is driven in rotational motion by means of the rod 6.

The bracket 12 is also adapted to support a motor 14 whose shaft is coupled through a reduction-gear unit 14a placed within the motor casing to a rod 16 which is fixed on the carriage 8 in parallel relation to the rod 6 and is also freely rotatable with respect to said carriage.

Each rod 6 and 16 is adapted to carry a toothed pinion 18, 20, both pinions being in mesh with a single ring-gear 22. The movement of rotation of the motor 14 is thus transmitted by the pinion 20, the ring-gear 22 and the pinion 18, then by the rod 6 and the sleeve 5 to the turntable 2 on which is placed a disc 24 to be analyzed.

The ring-gear 22 is also coupled by means of its shaft 23 and an electromagnetic clutch unit 26 to the shaft 28 of a pinion 30, said pinion being in mesh with a toothed rack 32 which is parallel to the turntable 2 and is carried by a frame 34 which supports the complete assembly. Said frame is closed and is provided at the top with an opening 36 through which the support 3 is permitted to pass, said support being screwed onto the endpiece 4.

The rotation of the motor 14 therefore causes the rotation of the ring-gear 22 and turntable 2 while producing at the same time the rotation of the pinion 30 and the displacement of this latter along the toothed rack 32.

Since the shaft 28 of the pinion 30 is coupled to the ringgear 22 by means of a clutch unit but is fixed laterally with respect to the carriage 8, the displacement of said pinion along the rack 32 causes the displacement of said carriage 8.

As shown in FIG. 3, the lower portion of the carriage is fitted on one side with wheels 38 which are intended to run on a strip 40 carried by the frame 34 and on the other side with grooved wheels 42 which are adapted to run along a rail 44, said rail being also carried by the frame 34.

The lateral motion of the carriage is accompanied by the lateral motion both of the motor 14 itself and the turntable 2 which is displaced at right angles to the electrode 1 while at the same time rotating about its own axis.

The carriage 8 is also fitted with a contact-strip 46 which is applied against an electric resistor 48 carried by a rectilineal rod 50 which is fixed in the frame 34 in parallel relation to the toothed rack 32, to the strip 40 and to the rail 44.

The contact-strip 46 is connected by means of a conductor 49 (shown in FIG. 4) to the unit which controls the rotation of the motor 14b whilst the resistor 48 is connected electrically be means of a conductor 52 on the one hand to a dynamo 140 which is driven by the motor 14b and on the other hand to an electric current generator G.

The output voltage of the dynamo is transmitted via a phase shifter 54 and the conductor 52 to the resistor 48 and via the same phase shifter 54 and a conductor 56 to the motor 14b. The rotation of said motor 14b is therefore controlled by a voltage which is a function of the difference between the output voltage of the dynamo 14c and the voltage derived from the potentiometer 46,-48, this difference being amplified by means of an amplifier 60. In fact, the position of the contactstrip 46 which is movable with the carriage 8 depends on the lateral displacement of said carriage, that is to say of the turntable and the filter. The voltage which istransmitted to the motor 141: is therefore a function of the difference between the output voltage of the dynamo and a reference voltage which is dependent on the position of the carriage 8.

As the lateral motion of the carriage takes place, the reference voltage is changed and in turn modifies the operation of the motor, namely the speeds of rotational and translational motion of the turntable. The product of these two speeds remains constant by virtue of the fact that both speeds are controlled in dependence on the position of the carriage 8.

It is thus possible to drive the turntable 2 by means of the reduction-gear unit 14a in such a manner as to ensure that the spiral S formed by the substances should progress at a constant speed in vertically opposite relation to the electrode 1 while having a constant pitch.

The analysis which is carried out by virtue of said device is thus extremely accurate. All points of the support are brought in turn vertically beneath the electrode and are subjected to identical conditions of excitation.

The device as hereinabove described has been employed for the analysis of particles which are present in the atmosphere and also for the analysis of solutions such as solutions of metallic salts or the like. For example, it has been observed that in the case of analysis of cobalt chloride, the limit of determination was reduced to IaIO I gImI. and that, at this limit, the reproducibility was still 9 percent.

The measurement which is taken by means of this device is therefore accurate, sensitive and reliable.

Without thereby departing from the scope of the invention, it would be possible to contemplate a number of different modifications to the embodiment which has been described by way of example in the foregoing. For instance, the filter or the flat solid to be analyzed could have any desired shape provided that the surface of this latter is comprised within the surface which passes beneath the electrode. Eventually, when the solid is electrically conductive, it can be itself connected to the high-voltage electric circuit.

We claim:

1. A device used in the excitation of substances for spectrographic analysis of said substances, comprising a vertical elec: trode, a turntable positioned under said electrode carrying the substance to be analyzed, a movable carriage supporting said turntable, a motor for rotating said turntable about a vertical axis parallel to said electrode and for driving said carriage in rectilineal translational motion at right angles to said electrode whereby all points of said turntable are moved in turn beneath said electrode along a spiral path and means for controlling the speed of rotation of said motor in dependence on the lateral displacement of said turntable for constant rate of transfer of said turntable beneath said electrode, said means for controlling the speed of rotation of said motor including an electric resistor, means for supplying a voltage to said resistor as a function of the speed of rotation of said motor and a movable electric contact whose position varies with the position of said carriage and of said turntable connecting said voltage sup lying means to said motor.

. A evlce in accordance with claim 1, said turntable being mounted on a shaft freely rotating on said carriage and driven by said motor, said motor being mounted on said carriage.

3. A device in accordance with claim 2, including a stationary toothed rack parallel to said turntable, a pinion engaging said rack and connected to said carriage for translational motion and a clutch unit coupling said pinion to said motor.

4. A device in accordance with claim 1, including a strip on said carriage forming an electric contact with said electric resistor, a support frame for the device, a rectilinear rod secured to said support frame and mounting said resistor. 

2. A device in accordance with claim 1, said turntable being mounted on a shaft freely rotating on said carriage and driven by said motor, said motor being mounted on said carriage.
 3. A device in accordance with claim 2, including a stationary toothed rack parallel to said turntable, a pinion engaging said rack and connected to said carriage for translational motion and a clutch unit coupling said pinion to said motor.
 4. A device in accordance with claim 1, including a strip on said carriage forming an electric contact with said electric resistor, a support frame for the device, a rectilinear rod secured to said support frame and mounting said resistor. 